The unbridled power and reach of China’s anti-corruption super agency have exceeded the initial fears of lawyers and academics in the four months since the new controversial system was introduced.

When Beijing set up the National Supervisory Commission in March, the most contentious issue was the commission’s power to detain anybody for investigation for up to six months without access to a lawyer.

But a recent case in the central Chinese province of Hunan has exposed how the commission’s activities could be used to deny detainees held by other law enforcement agencies access to legal counsel, even over unrelated offences.

The example has prompted lawyers and legal scholars to call for urgent official checks on the super agency’s “bloated power” under the National Supervision Law introduced in March.

The practice came to light this week when police stopped Chen Jieren, an outspoken political commentator and former journalist, and his family from meeting their lawyers while in custody, on the grounds that the local supervisory commission have launched an investigation into them for suspected bribery.

Chen, his wife and two brothers were put under “residential surveillance at a designated location” – a form of secret detention – by police in Hunan this month, on suspicion of extortion and running an illegal business, according to their lawyers.

Zhang Lei, a lawyer for one of Chen’s detained brothers, said that when the lawyers went to the police to request a meeting with Chen and others, they were told it was impossible.

According to Zhang, the police had asked the commission’s municipal wing if Chen and his family could meet their lawyers. The commission replied that it had launched a bribery investigation into them on July 4 and so no meeting with lawyers was allowed.

“The police showed us the supervisory commission’s written reply,” Zhang said. “Since the National Supervision Law has just come into force, we’re still trying to figure out if such a practice is legal or not.”

Chen is known for being outspoken and in the week leading to his detention, posted two articles on his blog critical of senior Communist Party officials in Hunan.

Since the system was proposed last year, the commission has been widely criticised by academics and rights advocates for its detention measure known as liuzhi, which denies detainees access to legal counsel.

But it was not known that suspects under investigation by the commission and its local branches could be denied meetings with lawyers in the earliest stages of a probe.

Wuhan University law professor Qin Qianhong said complete denial of legal access had become common practice in the past few months.

“The current understanding and practice is that once the supervisory commission launches an investigation, legal counsel will not be allowed,” Qin said.

“This means that suspects are not only denied access to a lawyer during the liuzhi phase, but throughout the whole operational process where the supervisory commission is involved.”

The National Supervision Law does not explicitly ban suspects’ access to lawyers, but Beijing has made it clear that the new supervisory commission will not be answerable to the Criminal Procedure Law, which grants suspects such rights in cases involving the police, prosecutors and courts.

Qin said the practice was problematic because it not only failed to protect the rights of suspects during investigations, but also contributed to the commission’s unchecked power.

The commission expands the party’s corruption-busting reach to all public servants on the government payroll, even if they are not party members. Non-public servants, such as Chen’s two brothers – a factory worker and a farmer – can also fall under its powers.

Qin said the commission loomed so large in the law enforcement system that some police used it as an excuse to deny access to suspects in custody, citing their suspected involvement in bribery.

He said that about a dozen lawyers, including a number from Beijing and Guangzhou, had consulted him on such cases.

The commission has been described by some critics as lending a veneer of legality to the party’s anti-corruption watchdog, the Central Commission for Discipline Inspection, and its long-criticised extra-legal measures. The two commissions share the same office and personnel, as do their various local branches.

Fu Hualing, a law professor at the University of Hong Kong who specialises in China’s legal system, said that if true, the supervision commission’s intervention in Chen’s police custody was illegal and a perfect example of the new agency’s “bloated power”.

“The [supervisory commission] does not have the right to command the police – the two organisations are totally separate and operate under different laws. There is no [direct supervisory] relationship between the two, at least legally, if not politically,” Fu said.

“The problem now is that the law and politics are entangled. The ‘New Era’ is an era where the law and politics cannot be separated – once something involves politics, the law does not have a say any more.”

Under China’s newly revised constitution, the supervisory commission has a status close to the cabinet and is ranked higher than the supreme court and top prosecutor’s office.

“Now they can lead the police; later they may lead the prosecutors by commanding which cases should proceed and what should be the penalty,” Fu said.

“In the future, will they try to lead the judiciary as well?”

“The supervisory commissions’ power must be confined to the cage of the National Supervision Law – it has already escaped the cage.”